This research program will continue to be directed towards obtaining a structural understanding of the mammalian hypothalamus, particularly towards elucidating as precisely as possible its pre- and post-synaptic arrangements. Light and electron transmission microscopic techniques will be used. The underlying assumption of the research is that hypothalamic neuropil can be analyzed, that it is not an unknowable, diffuse reticulum. Consequently it will be essential (1) not only to identify hypothalamic afferents but to determine their particular distribution and terminal patterns; (2) to describe the post-synaptic configurations of hypothalamic neurons; (3) to analyze the synaptic relations between the pre- and post-synaptic elements in hypothalamus; (4) to demonstrate the axonal projections of hypothalamic neurons and (5) to gain an idea about which of the neurons primarily are involved with particular hypothalamic functions (e.g. synthesis of corticotropic releasing factors). The immediate goal of this research will be to provide structural data needed (1) to understand hypothalamic function, and consequently, dysfunction, (2) to evaluate critically endocrinological and physiological data concerning hypothalamus. Additionally the resulting structural paradigms arrived at for the mature hypothalamus will provide information necessary for studies on the structural and functional development of this brain area. Hopefully this research will indicate new approaches for additional anatomical and physiological experiment attempting to define the role of the hypothalamus in behavior. The ultimate sum of this program remains to be the gathering of structural data necessary for understanding the biological bases of drive, motivation and behavior. BIBLIOGRAPHIC REFERENCES: Millhouse, O.E., Lining of the third ventricle in the rat, in Knigge, K.M., Scott, D., Kobayashi, H. and Ishii, S. (eds.), "Brain-Endocrine Interaction II," Karger, Basel, 1975, pp. 3-18. Batty, H.K. and Millhouse, O.E., Ultrastructure of the Gunn rat substantia nigra. I. Cytoplasmic changes, Acta Neuropathologica (in press)